Dear Ole Mechanic;

In one of your columns you talked about a coolant leak from a cracked head leading to engine bearing failure.  What I want to know is how a coolant leak could cause engine bearing failure?  I don't see how that could happen.

Coolant Puzzled


Dear Puzzled;Oil Being Poured

Right off, I will tell you that I am not sure if the ethylene glycol in antifreeze reacts with bearing material in a chemical reaction or with an electrolysis etching.  What I can tell you is that I have seen the results from antifreeze circulation with the engines lubricating oil.  The bearings are eaten away and they are shot!

Now you might ask how a crack in the combustion chamber could get antifreeze in the oil, because normally the combustion chamber has more pressure in it than there is in the cooling system.  That is very true, and usually combustion gases get into the cooling system and cause overheating--another thing that can kill an engine.  But when the engine is shut off, the pressure in the cooling system does force antifreeze down on top of a piston.  Once on top of the piston, it will find its way past the piston ring end gaps and into the crankcase.  Don’t forget that oil floats on top of water and on top of antifreeze, which should be 50-percent water.  OK, with the oil on top and the antifreeze on the bottom, I will remind you that the oil pump pickup is located at the bottom of the pan.  That is so that when you forget to check the oil and let it get two quarts low, the pump can still pick up the oil to lubricate the engine.  What all this means is that a very small amount of antifreeze in the pan will result in some antifreeze being pumped into the lubrication system.  The lubrication system then delivers the antifreeze and oil mixture to the camshaft bearings, the main crankshaft bearings and the connecting rod bearings.  The antifreeze then reacts with the bearing material and ruins them in short order.  There is a newer antifreeze called DexcoolŽ  that does not contain ethylene glycol, it contains organic acids.  Also, some other antifreeze mixtures use propylene glycol.  I am not sure if these acids or other glycol compounds react with bearing materials or not. 

That brings me to the second way that antifreeze, or plain water for that matter, can cause bearing failure.  If there is enough antifreeze/water in the oil pan, the oil pump pickup will pickup only antifreeze/water.  Neither of these has enough lubricating properties to lubricate the bearings.  Without proper lubrication, the bearings will overheat and seize to the crankshaft and ruin the bearings.  That usually ruins the crankshaft also.

Now a crack on the outside of an engine will leave a spot of coolant on the driveway.  That is not nearly as damaging to an engine as a crack on the inside that allows coolant to get into the oil.  The one problem that the coolant puddle in the driveway will cause is dead pets!  If ethylene glycol is lapped up by a cat or a dog, it will shut down the liver/kidneys and the animal will suffer a very excruciating painful death over several days.  Unfortunately, ethylene glycol is sweet tasting and most animals will drink more than enough to kill them.  No animal deserves to die from antifreeze poisoning, so never leave antifreeze in an open pan!!  OK, that’s my public-service announcement for this time.

Herr Professor Nuzanbolts